1. Field of the Invention
The present invention relates to vehicle-mounted devices and peripheral vehicle position calculation methods, and more particularly, to a vehicle-mounted device and a peripheral vehicle position calculation method for calculating positions of peripheral vehicles on the basis of information received from the peripheral vehicles via inter-vehicle communication and for performing predetermined processing based on the positions of the peripheral vehicles.
2. Description of the Related Art
Development in communication technologies has enabled communication among moving objects, such as vehicles, (referred to as inter-vehicle communication). For example, Bluetooth™, radio local area networks (LANs), and other means are available as inter-vehicle communication means.
Bluetooth™ is a radio link technology intended to be used as a cable replacement between electronic devices of a moving body and a fixed apparatus or between electronic devices of a moving body and another moving body. Bluetooth™ performs data packet transmission by a time-division duplex (TDD) system of a slot length of 625 μs and employs a frequency-hopping technique in which the frequency changes for each packet. For communication via Bluetooth™, a master makes inquiries about the types of slaves existing near the master using IQ packets, and each of the slaves existing near the master answers with a Bluetooth device address and clock information necessary for connection establishment using a frequency hopping sequence (FHS) packet. In other words, by making the inquiries, device addresses and clock information of all the slaves that answer the inquiries can be collected. The Bluetooth device address is a unique address given to all the Bluetooth apparatuses. Then, the master performs “Page” processing using a Bluetooth device address and clock information of a selected predetermined slave so that connection between the master and the slave is actually established to transfer data.
In contrast, in an AdHoc network using a radio LAN (autonomous distributed network), each mobile station has a unique address (for example, an internet protocol version 6 (IPV6) address). In order to create a network, a source station regularly sends checking signal waves including its own address. Destination stations receive the checking signal waves, and send answer signals including their own addresses to the source station. The source station receives the answer signal waves, and identifies peripheral stations that can communicate with the source station. The identified stations are collected and stored. Accordingly, the network is created to perform communication.
A technology for accurately notifying a passenger of a source vehicle about a positional relationship between the source vehicle and peripheral vehicles by acquiring positions of the peripheral vehicles in real time via inter-vehicle communication using the inter-vehicle communication means described above is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 11-195196.
However, in order to acquire positions of peripheral vehicles in real time with high accuracy via inter-vehicle communication using an AdHoc network, a Bluetooth network, or the like, each of the peripheral vehicles must broadcast the current position (longitude and latitude information), vehicle speed information, and traveling direction information at frequent intervals. Thus, a communication band is congested in proportion to an increase in the number of peripheral vehicles constituting the network. In other words, positional information cannot be communicated with high accuracy in a limited communication band. In order to communicate positional information with high accuracy, a wider band must be allocated for such inter-vehicle communication. However, this is not possible under the current communication scheme.